Heavy snow on top of leftover Thanksgiving ice storm results in avalanche warning
December 22, 2014
Avalanche safety courses
Colorado Mountain College’s Alpine Campus in Steamboat Springs offers a Level 1 avalanche safety course in its collection of "snow and ice" courses.
Steamboat Springs — The Colorado Avalanche Information Center issued an avalanche warning Monday for the Steamboat and Flat Tops zones along with all of the state's mountain ranges north of the San Juans and Sangre de Cristos.
The CAIC rated the danger high at all elevations and aspects and advised that "travel in avalanche terrain is not recommended." The avalanche warning will remain in place until 4 p.m. Tuesday, after unusually dense snow that was driven by high elevation winds fell on the Park Range near Steamboat Springs on Sunday.
"Temperatures were on the rise as this new snow fell, meaning a classic upside down storm has developed," veteran CAIC forecaster Scott Toepfer wrote early Monday morning. "This places heavier/denser snow on top of (drier), less dense snow, which is always a dangerous pattern in the development of avalanches, especially when it all sits on the November ice crust."
On Monday morning, Steamboat Ski Area reported 9 inches of fresh snow in 24 hours and 12.5 inches in 48 hours at the summit.
There has been one confirmed report of a human-triggered avalanche close to Steamboat in the past seven days. Routt County resident Joe Messina posted a written report on the CAIC website Thursday after entering the backcountry north of the boundary of Steamboat Ski Area.
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"Put in a ski cut in the Third Pitch area outside ski area," Messina wrote. "The slope released: about 14-inch crown, 50 feet wide, about 200 feet down the hill. Bed surface was the ice layer you've heard so much about. Weak layer is the interface between faceted crystals and the 1-2 centimeter Thanksgiving ice layer."
Messina was referring to a weather event that occurred on the night of Nov. 26. That's when freezing rain fell on top of 18 to 24 inches of fresh powder in the Park Range, resulting in a hard layer of ice on the surface.
Since Messina wrote that report, the dense snow that fell Sunday further has stressed the weak layers in the snowpack.
"Natural avalanches are likely Monday, human-triggered avalanches are very likely," Toepfer wrote.
Colorado Mountain College avalanche safety instructor Cody Perry ventured into some of his preferred skiing locations in North Routt County on Monday and concluded that the snow in the vicinity of Hahn's Peak is very different from conditions closer to Steamboat.
The new snow "is remarkably well bonded to itself, but it's really hard to tell how much new snow has fallen. Because of the wind, it's hard to tell what's new and what's a few days old," Perry said. "It just goes to show this year's pattern has led to a highly variable composition. The snowpack structure is complex, and that's typical for Colorado."
Perry's group did not observe any signs of recent avalanche activity.
Longtime Steamboat weather observer Art Judson said Monday morning that the snow that fell at his home between downtown Steamboat Springs and the ski area in the preceding 24 hours was the densest "dry snow" he has ever measured since 1993, the date he began recording every weather event. He uses the term dry snow to signify that it was not slush.
The 0.185 density means the snow that fell was 18.5 percent water. Another way to describe it would be to say that it would take only 5.4 inches of snow to equate to 1 inch of moisture.
Putting that in perspective, Judson said Steamboat's average snow density throughout many years is 7.2 percent, requiring 13.9 inches of snow to yield an inch of water.
Weather stations east of the city of Steamboat recorded anywhere from 3.6 to 6.1 inches of fresh snow Monday morning.
Ironically, Judson also recorded one of the driest snowfalls he has ever measured here Nov. 12. The 1 inch of new snow on his snow stake that morning contained 0.01 inch of water content, hence there would have to have been 100 inches of snow to yield an inch of water.